This application claims the priority benefit of Taiwan application serial no. 90113545, filed Jun. 5, 2001.
1. Field of Invention
The present invention relates to a light-emitting diode (LED). More particularly, the present invention relates to a group III-V element-based light-emitting diode with electrostatic discharge (ESD) protection capacity.
2. Description of Related Art
In recent years, group III-V nitride-based semiconductor materials have been used to produce light in the blue and ultraviolet range as well as high-temperature electronic devices. The material is quite versatile in the opto-electronic field. In particular, the group III-V group nitride-based semiconductor materials such as GaN, GaAlN, InGaN are suitable for fabricating light-emitting diodes. FIG. 1 is a schematic cross-sectional view of a conventional light-emitting diode constructed using group III-V nitride semiconductor material.
As shown in FIG. 1, the light-emitting diode is formed over a transparent substrate such as an aluminum oxide (Al2O3) layer. A nucleation layer 12 and an n-type conductive buffer layer 14 are sequentially formed over the substrate 10. The n-type buffer layer 14, for example, can be an n-doped gallium nitride (GaN) that facilitates subsequent crystal growth. A light-emitting active layer 18 is formed above the buffer layer 14. In general, a confinement layer or cladding layer 16 and 20 are formed, one above the active layer 18 and one below the active layer 18. The upper and the lower confinement layers (16 and 20) are doped using dopants of opposite polarity. In FIG. 1, the lower confinement layer 16 is an n-doped aluminum-gallium-nitride (AlGaN) layer while the upper confinement layer 20 is a p-doped aluminum-gallium-nitride (AlGaN) layer. A contact layer 22 is also formed over the upper confinement layer 20. The contact layer 22 can be a p-type gallium nitride (GaN) layer, for example. An electrode 24 serving as an anode of a diode is formed over the contact layer 22. In addition, another electrode 26 that serves as a cathode of the diode is formed over the buffer layer 14 in a region isolated from the lower confinement layer 16, the active layer 18 and the upper confinement layer 20.
FIG. 2A is a schematic circuit diagram showing a silicon-based shunt diode connected in parallel with a light-emitting diode (LED) to protect the LED against damages due electrostatic discharge. To prevent any damages to the light-emitting diode 30 due to electrostatic discharge (ESD) during operation, a silicon diode 40 is connected in parallel with the LED 30. Since the silicon diode 40 operates in the breakdown region, the diode 40 is always in a conductive state. If a normal forward bias voltage is applied to the two terminals V+ and Vxe2x88x92 of the LED 30, carrier passing through the p-n junction of the LED 30 produces a forward current that generates light. When an abnormal reversed voltage appears or there is an electrostatic discharge, excess voltage is discharged through the diode 40 operating in the breakdown mode. Since the discharge path goes through the second diode 40 instead of going through the LED 30, the LED 30 will not be damaged due to the presence of an abnormal voltage or electromagnetic discharge, which would causes the unrecoverable damage.
FIG. 2B is a schematic cross-sectional view of the LED in FIG. 2A with a silicon diode. According to the conventional method, the LED system is implemented using a flip-chip structure. As shown in FIG. 2B, the light emitting diode 30 includes a transparent substrate 32, an n-doped gallium nitride (GaN) layer 34, a p-doped gallium nitride (GaN) layer 36 and a pair of electrodes 38a and 38b. The diode 40 includes an n-doped silicon layer 42, a p-doped silicon layer 44 and a pair of metallic layers 46a and 46b. Areas 50a and 50b contain solder material. Through the solder material, the p-doped silicon layer 44 is electrically coupled to the n-doped gallium nitride layer 34 and the n-doped silicon layer 42 is electrically coupled to the p-doped gallium nitride layer 36. Thus, the structural layout shown in FIG. 2B produces the equivalent circuit shown in FIG. 2A.
A forward bias voltage is applied to the V+ terminal and the Vxe2x88x92 terminal in a normal operation. Hence, current flows from the p-doped gallium nitride layer 36 to the n-doped gallium nitride layer 34 so that generated light passes through the transparent substrate 32. When an abnormal reversed voltage appears or there is an electrostatic discharge, discharge current will pass from the n-doped silicon layer 42 to the p-doped silicon layer 44 without going through the main body of the light-emitting diode 30.
Although the aforementioned system is capable of minimizing damages to the light-emitting diode that result from an electrostatic discharge, the structure is difficult to manufacture. As shown in FIG. 2B, the light-emitting diode 30 section of the structure has to flip over the silicon diode. Not only is the structure difficult to fabricate, but mass production is also costly. Moreover, any deviation from alignment during package may result in a lower light-emitting power or device failure.
Accordingly, one object of the present invention is to provide a group III-V element-based light-emitting diode structure having electrostatic discharge protection capacity. The structure includes a reverse bias operating diode formed on the same side of a transparent substrate as the light-emitting diode so that manufacturing is simplified.
A second object of the present invention is to provide a group III-V element-based light emitting diode having a flip-chip structure and electrostatic discharge protection capacity. The structure incorporates a Schottky diode or a shunt diode so that electrostatic discharge protection capacity is enhanced.
A third object of the present invention is to provide a group III-V element-based light emitting diode having a flip-chip structure and electrostatic discharge protection capacity. The structure not only reduces processing steps, but also increases light-emitting power of the light-emitting diode.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a group III-V element-based light emitting diode having electrostatic discharge protection capacity. The structure includes a transparent substrate, a nucleation layer, a conductive buffer layer, a first confinement layer, an active layer, a second confinement layer, a contact layer, a first electrode, a second electrode, a third electrode and a fourth electrode. The nucleation layer is formed over the transparent substrate. The nucleation layer is a composite layer that includes a first nucleation layer and a second nucleation layer. The first nucleation layer and the second nucleation layer are isolated from each other. Similarly, the conductive buffer layer is a composite layer that includes a first conductive buffer layer and a second conductive buffer layer. The first conductive buffer layer and the second conductive buffer layer are formed over the first nucleation layer and the second nucleation layer, respectively. The first confinement layer, the active layer, the second confinement layer and the contact layer are formed over the first conductive buffer layer.
The first confinement layer is above the first conductive buffer layer and both layers are doped identically. The active layer is above the first confinement layer. The active layer is a semiconductor material layer containing doped group III-V nitride-based materials. The second confinement layer is above the active layer. The second confinement layer contains dopants that are different from the dopants in the first confinement layer. The contact layer is above the second confinement layer. The contact layer contains dopants identical to the dopants in the second confinement layer.
The first electrode serving as an anode of the light-emitting diode is above the contact layer. The second electrode serving as a cathodeof the light-emitting diode and the first conductive buffer layer are in contact but they are isolated from the first confinement layer, the second confinement layer, the active layer, the contact layer and the transparent substrate. The third electrode is above the second conductive buffer layer. The third electrode and the second conductive buffer layer together form a Schottky contact. Furthermore, the third electrode couples electrically with the second electrode. The fourth electrode is above the second conductive buffer layer but is isolated from the third electrode. The fourth electrode couples electrically with the first electrode.
This invention also provides a group III-V element-based light emitting diode having electrostatic discharge protection capacity. The structure includes a transparent substrate, a nucleation layer, a conductive buffer layer, a doped region, a first confinement layer, an active layer, a second confinement layer, a contact layer, a first electrode, a second electrode, a third electrode and a fourth electrode. The nucleation layer is formed over the transparent substrate. The nucleation layer is a composite layer that includes a first nucleation layer and a second nucleation layer. The first nucleation layer and the second nucleation layer are isolated from each other. Similarly, the conductive buffer layer is a composite layer that includes a first conductive buffer layer and a second conductive buffer layer. The first conductive buffer layer and the second conductive buffer layer are formed over the first nucleation layer and the second nucleation layer, respectively. The first confinement layer, the active layer, the second confinement layer and the contact layer are formed over the first conductive buffer layer. The doped region is inside the second conductive buffer layer interfacing with the surface of neighboring second conductive buffer layer to form a p-n junction diode.
The first confinement layer is above the first conductive buffer layer and both layers are doped identically. The active layer is above the first confinement layer. The active layer is a semiconductor material layer containing doped group III-V nitride-based materials. The second confinement layer is above the active layer. The second confinement layer contains dopants that are different from the dopants in the first confinement layer. The contact layer is above the second confinement layer. The contact layer contains dopants identical to the dopants in the second confinement layer.
The first electrode serving as an anode of the light-emitting diode is above the contact layer. The second electrode serving as a cathode of the light-emitting diode and the first conductive buffer layer are in contact but they are isolated from the first confinement layer, the second confinement layer, the active layer, the contact layer and the transparent substrate. The third electrode is above the doped region inside the second conductive buffer layer. The third electrode and the second conductive buffer layer together form a p-n junction diode. Furthermore, the third electrode couples electrically with the second electrode. The fourth electrode is above the second conductive buffer layer but is isolated from the third electrode. The fourth electrode also couples electrically with the first electrode.
The present invention also provides a group III-V element-based light emitting diode having a flip-chip structure and electrostatic discharge protection capacity. The aforementioned two group III-V element-based light emitting diode structures are interlocked together using a flip-chip process on an insulating substrate. The first electrode and the fourth electrode are connected to a first metallic film through a solder material so that the first electrode and the fourth electrode are electrically coupled. The first electrode and the fourth electrode couples with the insulating substrate via the first metallic film. Similarly, the third electrode and the second electrode are connected to a second metallic film through a solder material so that the second electrode and the third electrode are electrically coupled. The second electrode and the third electrode couples with the insulating substrate via the second metallic film. The first and the second metallic film can be the copper film on a printed circuit board. With the light-emitting diode overhanging the insulating substrate, light produced by the light-emitting diode is able to shine through the transparent substrate. Hence, light-emitting power is increased while damages due to electrostatic discharge are reduced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.